Osmotic fluid purification and draw compounds thereof

ABSTRACT

Draw compounds and draw solutions comprising said draw compounds for use in forward osmosis solvent purification systems. The draw compound may be a linear random, sequential, or block molecular chain consisting of at least one oxide monomer or diol monomer and have a temperature-dependent affinity with a feed solvent. The draw compound may further include a first terminal group and a second terminal group, at least one of the first terminal group and the second terminal group selected from the group consisting of a hydroxyl group, an amine group, a carboxylic group, an allyl group, and a C1 to C14 substituted and unsubstituted alkyl group. The draw compound may also be a branched random, sequential, or block molecular chain consisting of at least one oxide monomer or diol monomer.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. Pat. Application No.16/327,037, entitled “Osmotic Fluid Purification and Draw CompoundsThereof,” filed on Feb. 21, 2019, which is a national stage entry ofPCT/US2017/057395 filed Oct. 19, 2017, which claims priority to U.S.Provisional Application No. 62/494,841, filed on Aug. 22, 2016, each ofthe aforementioned applications is incorporated herein in its entirety.

FIELD OF TECHNOLOGY

The present disclosure is directed to the purification, decontamination,or desalination of sea water, brackish water, waste water, industrialwater, produced water and/or contaminated water using thermal sensitivedraw compounds for osmotic fluid purification. The present disclosure isfurther directed to draw compounds for forward osmosis for inorganic,organic, ionic, and/or polymeric fluids or solutions in which the soluteis separated, concentrated, or recovered from the solvent by an osmoticprocess.

BACKGROUND

Fluid purification and treatment is widely used in industrialapplications. Fluids suitable for fluid purification may includesolutions having both dissolved solids (solutes) and liquid components(solvents), and sometimes containing suspended solid particles. A fluidmay be an inorganic, organic, ionic, and/or polymeric solution, or amixture of the above. Often the solute in a fluid is sought after forits industrial and consumer value, but in many cases the solvent is theproduct of use. With industry and society becoming more and moreconscious of conservation and environmental issues, the separation,concentration, and recovery of both solute and solvent in a cost andenergy efficient way is an important field.

One effective fluid purification and treatment process is an osmoticprocess wherein the separation, concentration, and recovery of thesolute and/or solvent are carried out by osmotic processes. Osmoticprocesses for fluid purification may include forward osmosis process. Ina forward osmosis process, the solvent is transported through asemipermeable membrane from the feed side to the draw side of themembrane. A draw solution having an osmotic pressure greater than thatof the feed solution is provided to the draw side of the membrane. Theforward osmosis process involves a natural phenomenon and requires noenergy consumption. The transport of the solvent from the low osmoticpressure feed side of the membrane to the high osmotic pressure drawside of the membrane continues until equilibrium in osmotic pressure isreached. Forward osmosis process has drawn interest due to thelikelihood of future water shortage and a corresponding increase indemand for cost effective fluid purification technologies. Sea water,brackish water or otherwise contaminated water may be purified bycausing water (solvent) to be transported through a semipermeablemembrane that rejects the dissolved salts and other contaminates (thesolutes) by using the osmotic pressure of the draw solution to pull thesolvent through the membrane.

In at least some instances, an ideal draw solute is characterized byhigh flux, low reverse solute diffusion, and easy regeneration.Furthermore, an ideal draw solute should be, at least in some instances,stable at standard operating temperature and pressure, chemically inert,biologically safe and environmentally friendly. In at least someinstances, an ideal draw solute may be a thermally sensitive oligomer orpolymer which can use waste heat to separate the oligomer or polymerfrom the solvent component while the draw solution can be reused. Thedraw solution may also be a natural compound, a “green material,” and/ora compound produced by green chemistry for health and safetyconsiderations intrinsic to water purification applications.

U.S. Pat. No. 5,679,524 to Chakrabarti described using temperaturedependent solubility of polymers in water to accomplish desalination ina liquid/liquid separation process. In the disclosed process, a nonionicsurfactant is mixed with sea water in an attempt to separate salt fromwater in a direct osmosis process. However, the salt partition andproduct water yield may be undesirably low in at least some instances.

U.S. Pat. No. 8,021,553 to Iyer describes a system using a retrogradesoluble polymer solute and a nanofilter for separation and recovery ofthe resulting solute micelles from the product water. Iyer specifiesdraw solutes with both a hydrophobic and hydrophilic component. Iyeralso discloses a semi-batch recovery of the solutes by collecting theprecipitated (or phase separated) draw solute on a nanofilter andrecovering the solute by back flushing the nanofilter. Such approachesmay be impractical due to the high solids loading on the membrane andthe resulting low flux achieved in the nano filtration step.

U.S. Pat. Application Publication No. 2012/0180919 to Kim et al.discloses a draw solute for forward osmosis comprising atemperature-sensitive oligomer compound. The temperature-sensitiveoligomer compound may comprise a structure unit derived from a monomerselected from N-isopropylamide (NIPAM), N,N-diethylacrylamide (DEAAM),N-vinylcaprolactam (VCL), and a combination thereof.

U.S. Pat. Application Publication No. 2013/0240444 to Jung et al.discloses a thermosensitive copolymer comprising a first repeating unithaving a temperature-sensitive oligomer and a second repeating unithaving an ionic moiety and a counter ion to the ionic moiety. While thecopolymerization of a second repeating unit having an ionic moietyimproves osmotic pressure, the copolymer disclosed may not possess asufficiently high osmotic pressure and high water flux for watertreatment such as for sea water desalination.

U.S. Pat. Application Publication No. 2014/0217026 to Han et al.discloses a method of manufacturing a polymer hydrogel for an osmosissolute consisting of cross-linking and polymerizing a zwitterionicmonomer and a temperature-sensitive monomer. While a polymer hydrogelsuch as the one disclosed is expected to reduce reverse diffusion of thedraw solute, the water flux from such a polymer hydrogel draw solute islow and the long term stability of the hydrogel is a serious problemlimiting its practical applications.

U.S. Pat. Application Publication No. 2015/0060361 to Jung et al.discloses a draw solute including an amino acid repeating unit with anionic moiety and a counter ion thereof. The disclosed draw solution hasthe advantage of being environmentally friendly and of a relatively lowlevel of toxicity. However, stability of the draw solute at elevatedtemperatures, water flux and reverse solute diffusion through thesemipermeable membrane need to be improved.

U.S. Pat. No. 9,216,917 to Carmignani, Sitkiewitz, and Webley describessystems and processes for forward osmosis water purification ordesalination, wherein the diluted draw solution stream is heated,agglomerated and cooled to produce a cooled single phase water richstream that is then further purified to produce a water product stream.

WO 2015/156404 to Fuchigami et. al. describes a temperature-sensitiveabsorbent having a cloud point, and being designed to agglomerate whenheated. This temperature-sensitive absorbent includes at least ahydrophobic portion and a hydrophilic portion, and is a block copolymerthat has a glycerol skeleton as the basic skeleton thereof, and thatincludes an ethylene oxide group and a group comprising propylene oxideand/or butylene oxide. Alternatively, the temperature-sensitiveabsorbent is a block copolymer that has a trimethyolpropane skeleton asthe basic skeleton thereof, and that includes ethylene oxide andbutylene oxide.

WO 2016/027865 describes a solvent separation system and method using athree step process and a thermal-phase-change-type of polymer. Thethermal-phase-change-type of polymers are linear polymers with amolecular weight from 300 to 10,000. More specifically, thethermal-phase-change-type of polymer is a copolymer of ethylene oxideand propylene oxide with one or more of the terminal hydroxyl groups,alkyl groups, a phenyl group, an allyl group.

There is a need for improved fluid purification and treatment systemsand processes, and in particular, for improved draw compounds andsolutions that may be used in forward osmosis system and process.Desirable properties of an improved draw compound may include exhibitinghigh flux, low reverse solute diffusion, easy regeneration, physical andchemical stability, and being safe and environmentally friendly.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present application are described, by way of exampleonly, with reference to the attached Figures, wherein:

FIG. 1 is an illustration depicting an exemplary forward osmosis system,device, and process, according to an example embodiment of the presentdisclosure;

FIG. 2 is an illustration depicting osmotic pressure measurements forexemplary salt and polymer solutions as well as simulated sea water(Instant Ocean), according to an example embodiment of the presentdisclosure;

FIG. 3 is an illustration depicting osmotic pressure measurements oflinear random copolymers, corresponding to the solutions of TL-1180,according to an example embodiment of the present disclosure;

FIG. 4 is an illustration depicting a phase diagram of the draw compoundof Example 11, according to an example embodiment of the presentdisclosure; and

FIG. 5 is a flow chart describing a method of using the presentlydisclosed draw compound to purify or treat a feed solution according toa forward osmosis process, according to an example embodiment of thepresent disclosure.

It should be understood that the various aspects are not limited to thearrangements and instrumentality shown in the drawings.

DETAILED DESCRIPTION

It will be appreciated that for simplicity and clarity of illustration,where appropriate, reference numerals have been repeated among thedifferent figures to indicate corresponding or analogous elements. Inaddition, numerous specific details are set forth in order to provide athorough understanding of the embodiments described herein. However, itwill be understood by those of ordinary skill in the art that theembodiments described herein can be practiced without these specificdetails. In other instances, methods, procedures and components have notbeen described in detail so as not to obscure the related relevantfeature being described. Also, the description is not to be consideredas limiting the scope of the embodiments described herein. The drawingsare not necessarily to scale and the proportions of certain parts havebeen exaggerated to better illustrate details and features of thepresent disclosure.

Several definitions that apply throughout this disclosure will now bepresented. The term “coupled” is defined as connected, whether directlyor indirectly through intervening components, and is not necessarilylimited to physical connections. The term “fluidically coupled” isdefined as connected, either directly or indirectly through interveningcomponents, and the connections are not necessarily limited to physicalconnections, but are connections that accommodate the transfer ofsolutions, dispersions, mixtures, or other fluids between theso-described components. The connections can be such that the objectsare permanently connected or reversibly connected. The terms“comprising,” “including” and “having” are used interchangeably in thisdisclosure. The terms “comprising,” “including” and “having” mean toinclude, but are not necessarily limited to, the things so described.

As used herein, the terms “purify,” “purified,” or “purification,” intheir various forms, refer to one or more processes that producesolvent, such as water, having at least an incremental increase inpurity and/or an incremental decrease in solute concentration orcontaminant concentration. As such, the terms “purify,” “purified,” or“purification,” do not necessarily refer to the production of solventhaving a particular purity or a particular solute concentration, rather,the terms are used to refer to the production of solvent having at leastan incremental increase in purity and/or an incremental decrease insolute concentration or contaminant concentration, resulting from thepresently disclosed methods and techniques.

As used herein, the term “stream,” in its various forms, including itsuse in the term “feed stream,” refers to a solution that may be flowedto or received in a portion or component of an apparatus or system ofthe present disclosure, and is not limited to solutions introduced intoan apparatus or system, or portion thereof, under continuous flow, butrather, may also include solutions received in an apparatus or systemfor a period of time, such as that which may be employed in a series ofbatch processes.

The present disclosure provides improved osmotic fluid purificationsystems and processes having draw compounds. According to at least oneaspect of the present disclosure, a draw compound with a linearstructure and/or a branched structure for forward osmosis is provided.The presently disclosed process may include providing a semipermeablemembrane and a feed solution comprising solvent and having a firstosmotic pressure on a feed side of the semipermeable membrane andproviding a draw solution comprising a draw solute and having a secondosmotic pressure on a draw side of the semipermeable membrane. Solventmay be transported from the feed side and through the semipermeablemembrane to produce a dilute draw solution on the draw side of thesemipermeable membrane. The diluted draw solution may be heatedsufficiently to initiate phase separation and produce a two phaseeffluent stream comprising a liquid phase of draw solute solution,containing the draw compound, and a liquid phase of water. The drawcompound is permitted to agglomerate in the diluted draw solution toproduce an agglomerated two-phase effluent stream comprising a liquidphase of agglomerated draw solute and a liquid phase of water. Theagglomerated draw solute is separated from the diluted draw solution toproduce a solvent rich stream, comprising residual draw solute andsolvent, and a solute rich stream, comprising agglomerated draw soluteand solvent. The solvent rich stream is cooled to produce a cooledsingle phase solvent rich stream comprising the residual draw solute.The residual draw solute is separated from the cooled single phasesolvent rich stream to produce a residual draw solute stream and apurified solvent product stream. By way of a non-limiting example, thesolvent may be water and the presently disclosed forward osmosis watertreatment system and process may be implemented to treat sea water,brackish water, industrial and municipal waste water, contaminatedwater, and the like.

The presently disclosed systems and processes for forward osmosis waterpurification or desalination initiate phase separation by heating. Theresulting dispersed two phase system is aggregated using a coalescer andthe bulk of the solute is recovered using a phase separator. Finally,the resulting water rich stream is cooled to dissolve any remainingdispersed solute and a single phase stream, or low solute concentration,is sent to a filter (e.g., nanofilter) for final, continuous, filtrationprocessing. The nanofilter is selected to reject the solute molecularbased on size or structure and ideally passes most of the dissolvedsalt. A solute free water filter permeate is the process product.According to at least one aspect of the present disclosure, thepresently disclosed systems and processes for forward osmosis waterpurification or desalination, may include those features and elements ofthe systems and devices disclosed in U.S. Pat. No. 9,216,917, which isherein incorporated by reference, in its entirety.

FIG. 1 illustrates a forward osmosis process, device, and system thatmay be used with the presently disclosed draw compounds and drawsolutions, according to an exemplary embodiment of the presentdisclosure. A brackish water source stream 1 is fed to a feed side of asemipermeable membrane in a forward osmosis module 3. A draw solutionstream 18 is fed to a draw side of a semipermeable membrane in theforward osmosis module 3. The osmotic pressure of brackish water sourcestream 1 is less than the osmotic pressure of the draw solution stream18. This pressure differential drives water from the brackish watersource stream 1 to permeate through the semipermeable membrane resultingin a dilute draw solution stream 5 and a brine stream 2.

The dilute draw solution stream 5 is passed through a heat exchangernetwork 4 where the temperature is increased sufficiently to initiatephase separation and supersaturate the dilute draw solution stream 5with solute. The heat exchanger network 4 can include one or more heatexchangers configured in series or parallel for increasing thetemperature of the dilute draw solution 5. The temperature of the dilutedraw solution stream 19 exiting as effluent from the heat exchangernetwork 4 is sufficient to create a two phase effluent.

The two phase draw solution effluent stream 19 exiting the heatexchanger network 4 is fed to a temperature controlled coalescer 6 toagglomerate small solute rich droplets in the heat exchanger network 4.The coalescer 6 is designed to aggregate solute rich drops large enoughto be separated in the subsequent phase separator process 8. In anexemplary embodiment, the coalescer 6 is designed to aggregate soluterich drops to greater than 10 µm, preferably greater than 25 µm and morepreferably greater than 50 µm. The pressure drop caused by two phaseflow streams passed through the coalescer 6 is significantly less thanpressure drop caused by two phase flow streams passed through ananofilter. The use of the coalescer 6 eliminates added complexity andback-flushing required in semi-batch operations.

The coalescer 6 can also be segregated into a top section comprisinghydrophobic coalescing elements for agglomerating the draw solute and abottom section comprising hydrophilic coalescing elements for wateraggregation. The degree of hydrophobicity of the hydrophobic coalescingelements and the degree of hydrophilicity of the hydrophilic coalescingelements are selected to achieve a specific degree of agglomeration ofthe draw solute to greater than 10 µm. In an exemplary embodiment, thedegree of hydrophobicity of the hydrophobic coalescing elements and thedegree of hydrophilicity of the hydrophilic coalescing elements areselected to agglomerate the draw solute to greater than 10 µm.

The coalescer effluent stream 7 is fed to a liquid phase separator 8wherein the solute rich drops from the coalescer 6 are accumulated. Theliquid phase separator 8 is designed to separate two or more immiscibleliquids or solutions. More particularly, the liquid phase separator 8 isdesigned to separate solute from water and produce a continuous soluterich stream 10 and a continuous water rich stream 9. The liquid phaseseparator 8 can be a temperature controlled gravity phase separator,centrifuge, hydro-cyclone or similar device. In at one embodiment of thepresent disclosure, the liquid phase separator 8 is a temperaturecontrolled gravity phase separator. In an exemplary embodiment, theoperating temperature of the coalescer 6 and liquid phase separator 8 ismaintained at less than 150° C. In other instances, the operatingtemperature of the coalescer 6 and liquid phase separator 8 may bemaintained at less than 100° C. and or less than 80° C. to establish aspecific concentration of the solute and osmotic pressure of the waterrich stream 9 exiting as effluent from the liquid phase separator 8. Inan exemplary embodiment, the operating temperature of the coalescer 6and liquid phase separator 8 is selected to establish a concentration ofsolute in the water rich stream 9 of less than 5%, or less than 2% orless than 1% by weight solute in solution.

In an exemplary embodiment, the liquid phase separator 8 is designed toconcentrate the solute in the solute rich stream 10 to a concentrationof greater than 60%, or greater than 80% or greater than 90% by weightsolute in solution. The solute rich stream 10 exiting the liquid phaseseparator 8 as effluent is cooled in a heat exchanger 16. The water richstream 9 exiting as effluent from the phase separator 8 is also cooledby a heat exchanger 11 to allow residual solute to redissolve and tocreate a single phase cooled water rich stream 12. The cooled water richstream 12 is a single phase stream fed to a nanofilter 13, ultrafilter,or reverse osmosis module including a semipermeable membrane or similardevice used to separate the residual solute from the product water. Thenanofilter 13 is selected to reject the solute molecules based on sizeor structure and ideally passes most of the dissolved salt. The finalfiltration step in the nanofilter 13, ultrafilter, reverse osmosismodule or similar device is used only for the recovery of the residualsolutes in the single phase cooled water rich stream 12. The solutes areredissolved in single phase cooled water rich stream 12 to minimizepressure drop across the nanofilter 13 and to simplify operation. Asolute free water filter permeate 14 is the process product.

The solute rich stream 15 exiting the nanofilter 13 is combined in amixer 17 with the cooled solute rich stream 10 exiting the heatexchanger 16 to create a combined solute rich stream 18 (that is, thedraw solution stream 18, above). The mixer 17 is used to completelydissolve the solute in the resulting combined solute rich stream 18. Thecombined solute rich stream 18 is fed to the forward osmosis module 3 topurify or desalinate the source stream 1 in a continuous manner. Thesolute rich stream 10 exiting the phase separator 8 as effluent iscooled in the heat exchanger 16 to a specific temperature that maintainsthe temperature of combined solute rich stream 18 sufficiently low andprovides complete solubility of the solute in the combined solute richstream 18 entering the forward osmosis module 3.

In an exemplary embodiment of FIG. 1 , the coalescer 6 and/or the phaseseparator 8 can be heated to operating temperature with an additionalexternal heat source (not shown).

In another exemplary embodiment of FIG. 1 , the coalescer 6 and phaseseparator 8 are combined into one physical device. Alternatively, thesurface area within the heat exchanger network 4 and the piping betweenthe heat exchanger network 4 and the phase separator 8 can be used inplace of the coalescer 6.

The draw compound may be an inorganic, organic, ionic, polymericcompound, or any combination thereof. More specifically, the drawcompound may be a temperature-sensitive inorganic, organic, ionic,polymeric compound, or any combination thereof. In at least someinstances, the suitable draw solute may be a temperature sensitiveorganic, oligomeric, polymeric compound which separates into a feedsolvent rich layer and a draw compound rich layer upon being heatedabove the phase transition temperature of the diluted draw solution.Depending on the density differentiation of the feed solvent rich layerand the draw compound rich layer, the feed solvent rich layer may floaton top or sink to the bottom of the containment vessel for easyseparation. The phase separation process concentrates the diluted drawcompound solution, thereby drastically increasing its osmotic pressureso the concentrated draw solution may draw the feed solvent through asemipermeable membrane in a forward osmosis process.

According to at least one aspect of the present disclosure, the drawsolute may be a temperature-sensitive oligomer or polymer. In suchcases, the temperature-sensitive polymer may be a linear, sequential,block, branching, graft, gradient, star, dendritic oligomer orcopolymer, or any combination thereof. In at least some instances, thetemperature-sensitive polymer may be a homopolymer, a linear random orblock copolymer, a branched random or block copolymer, or anycombination thereof. The composition, structure, and architecture of thetemperature-sensitive polymer may be designed to optimize its osmoticpressure and flux, and minimize reverse diffusion, as well as theresidual amount of the draw compound in the separated feed solventstream. Preferably, the starting compound and repeating unit of thetemperature-sensitive draw solute may be selected from green compoundsand natural compounds to ensure that the draw solute is not toxic tohuman, animal, and marine life.

According to at least one aspect of the present disclosure, thetemperature-sensitive draw compound may be a linear random and/or blockpolyethylene oxide-polypropylene oxide oligomer or polymer. In at leastsome instances, the temperature-sensitive polymer may be a linear randomand/or block polyethylene oxide-polypropylene oxide-polybutylene oxidecopolymer. The composition and monomer ratio may be selected to optimizeosmotic pressure and flux while minimizing reverse diffusion as well asthe residual amount of the draw compound in the separated feed solventstream. The terminal group of the draw compound may be capped withmethyl, ethyl, propyl, butyl, phenyl, and other aryl groups.

According to at least one aspect of the present disclosure, thetemperature-sensitive draw compound may be a branched random and/orblock polyethylene oxide-propylene oxide oligomer or polymer. In atleast some instances, the temperature-sensitive draw compound may be abranched random and/or block polyethylene oxide-propylene oxide-butyleneoxide oligomer or copolymer. The branching structure and architecturehas shown significant improvement in reducing reverse solute diffusionthrough the front forward osmosis membrane and through the back nanofiltration and reverse osmosis (RO) membranes in comparison to thelinear polymer. Similarly, the terminal group of the branching polymermay be capped with methyl, ethyl, propyl, butyl, phenyl, and other arylgroups.

According to at least one aspect of the present disclosure, the drawsolution comprising the temperature-sensitive compound exhibits anosmotic pressure higher than that of the feed fluid, which enables thetransfer of the solvent from the feed fluid through a semipermeablemembrane or re-partitioning of the solvent in the mixture of drawsolution and feed solution. The affinity between thetemperature-sensitive draw compound and the solvent weakens as thesolution comprising the draw compound and the solvent is heated orcooled, resulting in phase separation or precipitation, thus providing away for effective fluid purification and treatment.

The presently disclosed draw solution and temperature-sensitive drawcompound may be used in the production of fresh water and waste watertreatment by the forward osmosis process by using thetemperature-sensitive draw compound to aggregate the heated or cooledaqueous solution. The temperature-sensitive draw compound may have acloud point that facilitates phase separates into a solute-rich phaseand a solvent-rich phase. In at least some instances, devices for waterpurification and/or waste water treatment may include the presentlydisclosed draw solution and temperature-sensitive draw compound.

In at least some instances, the temperature-sensitive draw compound maybe a linear random, sequential, and/or block oligomer or polymer whichmay be represented by the follow general formula

wherein A is an oligomer or polymer segment with statistically random,sequential, and/or block structure, R₁ and R₂ are terminal groups ofhydrogen, hydroxyl, carboxylic, amine, allyl, phenyl, and a substitutedor unsubstituted C1 to C14 alkyl groups.

The structure element A may be an oligomer, homopolymer, and copolymerof epoxides and cyclic ethers comprising ethylene oxide, propyleneoxide, 1,2-epoxy-butane, 2,3-epoxy-butane, styrene oxide,epiflurohydrin, epichlorohydrin, tetrahydrofuran, oxetane, dioxolane,trioxane, butyl glycidyl ether, phenyl glycidyl ether, allyl glycidylether, and the like. Similarly, the structure element A may also be anoligomer, homopolymer, and copolymer of diols comprising 1,2-ethanediol,1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol,substituted diols such as 2-methyl-2-propyl-1,3-propanediol andneopentyl glycol, aromatic diols such as resorcinol and4,4′-(propane-2,2-diyl)diphenol, and the like.

In at least some instances, the structure element A may compriseethylene oxide and propylene oxide, and the temperature-sensitive drawcompound may be represented by the formula

wherein the terminal groups R₁ and R₂ are hydroxyl groups, the formulabecomes

In at least some instances, the temperature-sensitive draw compound maybe a linear random, sequential, and/or block copolymer of ethyleneoxide, propylene oxide, and butylene oxide, and may be represented bythe following formula

wherein R₁ and R₂ are terminal groups selected from the group consistingof hydrogen, hydroxyl, carboxylic, amine, allyl, phenyl, and asubstituted or unsubstituted C1 to C14 alkyl groups.

In at least some instances, the temperature-sensitive draw compound maybe a branched random, sequential, and/or block copolymer which may berepresented by the general formula

wherein S is a starting compound which reacts with monomers such asethylene oxide, propylene oxide, butylene oxide, and the like; A₁, A₂,A₃, and A_(n) are the branching elements and each may be a random,sequential, and/or block structure itself; R₁, R₂, R₃, and R_(n) areterminal groups of hydrogen atom, hydroxyl, carboxylic, amine, allyl,phenyl, and a substituted or unsubstituted C1 to C14 alkyl groups.

Suitable starting compound S for the preparation of branchedtemperature-sensitive draw compounds has 3 or more functionality intheir molecular structure, which may include, but is not limited to,polyols, polyamines, polycarboxylic acids, and the like. The startingcompound itself may have a linear or ring structure, may be hydrophobicor hydrophilic, and may be flexible or rigid to optimize flux andminimize reverse solute diffusion. In some instances, the startingcompounds may be polyols, such as glycerol, trimethylolpropane,pentaerythritol, diglycerol, ditrimethylolpropane, phloroglucinol,sorbitol, sorbitan, glucose, fructose, and methyl glucoside. Forportable water, sea water desalination, and environmental friendly fluidtreatment systems, the preferred starting compound is a green substanceor natural compound, and more preferably is a food grade compound whichincludes, but is not limited to, vitamins such as ascorbic acid andsugar alcohols. Suitable sugar alcohols may include, but is not limitedto, glycerol for the preparation of 3-arm branched draw compound;erythritol and threitol for the preparation of 4-arm branched drawcompound; arabitol, ribitol, and xylitol for the preparation of 5-armbranched draw compound; fuctitol, galacititol, iditol, inositol,mannitol, and sorbitol for the preparation of 6-arm branched drawcompound; and volemitol, isomalt, maltitol, lactitol for the preparationof 7-arm and more branched draw compound.

The structure elements A₁, A₂, A₃, and A_(n) in Formula 2-1 may beselected from the group consisting of oligomer, homopolymer, andcopolymer of epoxides and cyclic ethers comprising ethylene oxide,propylene oxide, 1,2-epoxy-butane, 2,3-epoxy-butane, styrene oxide,epiflurohydrin, epichlorohydrin, tetrahydrofuran, oextane, dioxolane,trioxane, butyl glycidyl ether, phenyl glycidyl ether, ally glycidylether, and the like. Similarly, the structure element A₁, A₂, A₃, andA_(n) in Formula 2-1 may also be an oligomer, homopolymer, and copolymerof diols comprising 1,2-ethanediol, 1,2-propanediol, 1,3-propanediol,1,4-butanediol, 1,5-pentanediol, substituted diols such as2-methyl-2-propyl-1,3-propanediol and neopentyl glycol, aromatic diolssuch as resorcinol and 4,4′-(propane-2,2-diyl)diphenol, and the like.Each of the structure elements may have the same or differentcomposition, molecular weight, chain length, and molecular architecture.

The simplest branched temperature-sensitive draw compound is a 3-armoligomer or polymer. The following Chemical Formula 2-2 and ChemicalFormula 2-3 illustrate the 3-arm branched oligomer and polymer withglycerol and trimethylolpropane as the starting compound.

Additionally, the branched temperature-sensitive draw compound may be a4-arm oligomer or polymer. For example, in at least some instances, thestarting compound may be penterythritol and the corresponding 4-armtemperature-sensitive polymer has a structure illustrated in thefollowing formula

Furthermore, a branched temperature-sensitive draw compound with 6-armstructure may be synthesized. In addition to a higher number of arms,the starting compound may have additional advantage to be a greensubstance and/or natural compound and may be selected from readilyavailable natural sugar alcohols such as sorbitol. Such an exemplary6-arm temperature-sensitive oligomer or polymer may be represented bythe formula below.

The presently disclosed oligomer or polymer draw compound may besynthesized in a laboratory and/or industrial batch reactor. In at leastsome instances, a linear/branched random or sequential ethyleneoxide-propylene oxide oligomer or polymer may be prepared by feedingpressurized ethylene oxide and propylene oxide into a stainless steelreactor. A strong base such as sodium hydroxide may be used as acatalyst to induce the ring opening polymerization and the reactiontemperature may be maintained between 120-175° C. Upon completion of thereaction, the resulting oligomer or polymer may be cooled down,neutralized, and filtered to remove impurities. Alternatively, alinear/branched block ethylene oxide-propylene oxide oligomer or polymermay be prepared by feeding the first reactant, which may be eitherethylene oxide or propylene oxide, into a batch reactor. Upon thecompletion of the ring opening reaction of the first reactant, a secondreactant may then be injected into the reactor to continue the chaingrowth process. The resulting ethylene oxide-propylene oxide blockcopolymer may then be cooled, neutralized, and filtered to removeimpurities.

The presently disclosed draw compounds may consist of various numbersand orders of monomers, which impact the required solution properties.Osmotic pressure, cloud point temperature, molecular weight, molecularstructure and architecture of the presently disclosed draw compounds maybe adjusted by adding or subtracting the various monomer units and/orchemical elements.

The branched temperature-sensitive draw polymer should have 3 or morebranches, or 3 or more arms, which allows it to be trapped and retainedeffectively by the open pores of a semipermeable forward osmosismembrane, reverse osmosis membrane, and nanofiltration membrane,resulting in low reverse solute diffusion. Depending on the length andstructure of the arms, the branched polymer may exhibit low viscosity incomparison to a linear polymer with an equivalent molecular weight,further enhancing molecular diffusivity and increasing flux.

The presently disclosed draw solutes may be temperature-sensitive innature. Upon exposure to a temperature change, such as heating orcooling, the solution may undergo phase separation to form a solute-richphase and a solvent-rich phase. The draw solution may have an uppercritical solution temperature (UCST) or a lower critical solutiontemperature (LCST) type phase diagram, depending on the applicationintended. In an UCST phase diagram, the solution has an upper criticalsolution temperature and the initially homogeneous solution phaseseparates below the phase separation temperatures. On the other hand, asolution exhibiting LCST phase behavior has a lower critical solutiontemperature and the initial homogeneous solution phase separates at atemperature above the phase separation temperatures. In a binary system,an LCST solution first separates into small domains of a solute-richphase and a solvent-rich phase at a temperature slightly above thecritical temperature. When the temperature is further raised and/orphase separation time is further prolonged, the small domains coalescetogether to form large domains in micro- to millimeter size. Dependingon the density difference, the heavy phase sinks to the bottom while thelight phase floats to the top, thus forms two distinct layers. It shouldbe appreciated that this solute and solvent separation process is both athermodynamic phenomenon and a kinetic process. The optimal design ofthermal phase separation fluid treatment process cannot be achievedwithout a thorough understanding of the relationship betweenthermodynamics and dynamics.

Since a solute-rich phase and a solvent-rich phase typically exhibitdifferent refractive indexes, the onset of the phase separation in abinary system may be detected by the appearance of cloudiness due to thescattering of light by the domains with characteristic dimension in therange of visible light wavelength. The temperature at which a solutionturns cloudy is defined as the cloud point for a temperature-sensitivecompound.

In at least some instances, the temperature-sensitive compound has aLCST type phase diagram. Depending on its cloud point and phaseseparation temperatures, the diluted draw compound solution exiting asemipermeable membrane may phase separate into a solute-rich phase and asolvent-rich phase at or below room temperature. While a low cloud pointdraw solution saves electric and thermal energy consumption, such a drawcompound and solution may not have a high osmotic pressure necessary foran osmotic fluid treatment system, in particular in forward osmosisprocesses. The cloud point of a draw solution thus needs to be selectedcarefully, and a draw compound has to be designed to have an appropriatecloud point to optimize performance in an osmotic fluid process.

The suitable cloud point of a draw compound is dependent on the intendedapplication. For potable water production and sea water desalination,the cloud point or phase separation temperature of the draw solution maybe in the range of from about 20° C. to about 100° C. In at least someinstances, the cloud point or phase separation temperature of the drawcompound may be in the range of from about 35° C. to about 80° C. Inother cases, the cloud point or phase separation temperature of the drawcompound may be in the range of from about 45° C. to about 70° C. On theother hand, for zero-liquid discharge (ZLD), the cloud point or phaseseparation temperature may be selected from about 50° C. to about 175°C. In other such cases, the cloud point or phase separation temperaturemay be selected from about 75° C. to about150° C. In still other cases,the cloud point or phase separation temperature may be selected fromabout 90° C. to about125° C. for zero-liquid discharge (ZLD) process andhigh salinity water treatment in oil-and-gas industry.

The presently disclosed draw compounds may have a useful working osmoticpressure at ambient conditions and at elevated temperatures. In at leastsome cases, the presently disclosed draw compounds have a high osmoticpressure. Referring to FIG. 2 , the osmotic pressure of simulated seawater (Instant Ocean) is approximately 320 psi with a 3.5% TDS (Totaldissolved solids) content. However, the TDS can be as high as 4.5% forsea water in the Middle East region and the corresponding osmoticpressure is approximately 400 psi. Generally speaking, a high water fluxis directly related to a high osmotic pressure of the draw solution.Therefore, in such cases, draw solutions comprising the draw compoundpreferably exhibit a high osmotic pressure across the working range ofconcentrations. For example, in sea water desalination, the osmoticpressure of the draw solution should be from about 400 psi to greaterthan 1200 psi in the regenerated concentrated state. In some cases, theosmotic pressure of the draw solution may be at least 400 psi in theregenerated concentrated state. In other instances, the osmotic pressureof the draw solution may be at least 700 psi in the regeneratedconcentrated state. In yet other instances, the osmotic pressure of thedraw solution may be at least 1200 psi at the regenerated concentratedstate. As used herein, the term “regenerated concentrated state” refersto the high concentration of the draw compound after thermally inducedphase separation. The term “regenerated concentrated state” may alsorefer to the high solute concentration of the draw compound in the drawsolution before the draw solution is fed into the semipermeable membranein forward osmosis process. For high salinity water treatment and ZLDprocess, the osmotic pressure of the draw solution may be from about1200 psi to about 3500 psi in the regenerated concentrated state. Inother instances, the osmotic pressure of the draw solution may be atleast 1200 psi at the regenerated concentrated state, in the case ofhigh salinity water treatment and ZLD systems. In still other instances,the osmotic pressure of the draw solution may be at least 2000 psi atthe regenerated concentrated state, in the case of high salinity watertreatment and ZLD systems. In yet other instances, the osmotic pressureof the draw solution may be at least 3500 psi at the regeneratedconcentrated state.

A high osmotic pressure stems from a strong interaction of the drawcompound with water molecules. It should be appreciated that a stronginteraction between the draw solute and the water molecules originatesfrom ionic force or hydrogen bonding. Additionally, the packing densityand/or steric hindrance of the water molecules and draw solute affectthe strength of the interaction to some degree. Taking intoconsideration these factors, it is possible to design and developappropriate classes of materials which have remarkably high osmoticpressure, i.e., at least 3000 psi at or close to solubility limit. Thetrouble, which should be understandable and appreciated by one of skillin the art, is that such a high osmotic pressure draw compound isdifficult to separate from water and no method is known for easy and lowcost regeneration of the draw compound.

The osmotic pressure of the presently disclosed draw compounds dependson the application and the desired recovery. The presently discloseddraw solutes require higher osmotic pressure for high recovery inapplications with process streams containing higher concentrations ofdissolved solids. The draw solution osmotic pressure required for theexemplary systems and processes for forward osmosis water desalinationof seawater is generally greater than ~400 psi, with greater than ~700psi being preferred to allow for reasonable product flux and recovery.

Furthermore, the presently disclosed draw compounds may have a highsolubility in the feed solvent as osmotic pressure generally increaseswith solute concentration. In at least some instances, the draw compoundmay have a solubility in the solvent of at least 20% in weightconcentration. In other cases, the draw compound may have a solubilityin the solvent of at least 50%. The presently disclosed draw compoundsmay be miscible with the solvent at any ratio. The solubility limitbecomes particularly important with the increasing molecular weight ofthe polymeric draw compound as the solute may start to precipitate outof the solution, thereby no longer contributing to the osmotic pressureof the said solution. In at least some instances, the presentlydisclosed draw solutes or compounds may have a strong solubilitydependence at the lower temperature range (e.g., close to 40° C.), whichmay be preferred so as to minimize the operating temperature of theregeneration steps in the process and to minimize resulting energy loss.

According to at least one aspect of the present disclosure, an ethyleneoxide-propylene oxide (EO-PO) copolymer may be used as the draw compoundfor portable drinking water production and sea water desalination. Themonomer ratio (EO/PO ratio) plays a critical role in material propertiesand membrane performance as the ratio affects osmotic pressure, cloudpoint, residual draw compound level in product water, and to a lesserdegree the reverse solute diffusion. The presently disclosed drawcompound may have a EO/PO ratio of from about 0.01 to about 10. In otherinstances, the draw compound may have a EO/PO ratio of from about 0.05to about 5. In still other instances, the draw compound may have a EO/POratio in the range of from about 0.1 to about 1. In at least someinstances, the draw compound may be an oligomer or low molecular weightpolymer having a low EO/PO ratio so as to meet the requirement of cloudpoint and phase separation temperatures.

The molecular weight of a draw compound affects the viscosity of thedraw solution. Additionally, solvent flux, residual draw solute level,and reverse solute diffusion are all related to the molecular weight. Itshould be appreciated that a low molecular weight inorganic and organiccompound is highly desired from viscosity point of view as such asolution provides the most reduction in viscosity compared to a highermolecular weight oligomer and polymer. However, such a low molecularweight inorganic and organic compound may exhibit a high reverse solutediffusion and often cannot be regenerated effectively. Therefore, themolecular weight has to be selected carefully and the corresponding drawcompound needs to have well balance performance. In at least someinstances, the molecular weight of the draw compound may be from about100 to about 25,000 in forward osmosis process. In other cases, themolecular weight of the draw solute may be from about 200 to 15,000. Inyet other cases, the molecular weight of the draw solute may be fromabout 300 to about 5,000. In still other cases, the molecular weight ofthe draw compound may be from about 500 to about 3,500 in forwardosmosis. While a low molecular weight is generally preferred, themolecular weight of the draw compound also needs to be high enough toallow effective polish filtering of the dissolved oligomer and polymerusing nanofilter and/or reverse osmosis membrane in the post-treatmentstep.

According to at least one aspect of the present disclosure, the drawcompound may be a narrow distributed linear or branched random orsequential oligomer or polymer chain comprising ethylene oxide monomerand propylene oxide monomer. In such cases, the draw compound may have amolecular weight from about 500 to about 1,200 and an EO/PO ratio offrom 0.1 to 10.0, and a cloud point temperature from about 20° C. toabout 100° C. According to this aspect of the present disclosure, thedraw compound may further be characterized by a residual content lessthan 0.5% upon phase separation, a reverse diffusion through forwardosmosis (FO) membranes of less than 0.1 GMH. According to this aspect,the oligomer or polymer chain may be temperature sensitive and have atemperature-dependent affinity with the feed solvent.

According to at least one aspect of the present disclosure, the drawcompound may be a narrow distributed linear or branched random orsequential oligomer or polymer chain comprising ethylene oxide monomerand propylene oxide monomer. In such cases, the draw compound may have amolecular weight from about 800 to about 3,500 and an EO/PO ratio offrom 0.05 to 5.0, and a cloud point temperature from about 50° C. toabout 175° C. According to this aspect of the present disclosure, thedraw compound may further be characterized by a residual content lessthan 0.5% upon phase separation, a reverse diffusion through forwardosmosis (FO) membranes of less than 0.1 GMH. According to this aspect,the oligomer or polymer chain may be temperature sensitive and have atemperature-dependent affinity with the feed solvent.

According to at least one aspect of the present disclosure, the drawcompound may be a narrow distributed linear or branched random orsequential oligomer or polymer chain comprising ethylene oxide monomerand propylene oxide monomer. In such cases, the draw compound may have amolecular weight from about 200 to about 5,000 and an EO/PO ratio offrom 0.1 to 1.0, and a cloud point temperature from about 20° C. toabout 100° C. According to this aspect of the present disclosure, thedraw compound may further be characterized by a residual content lessthan 0.5% upon phase separation, a reverse diffusion through forwardosmosis (FO) membranes of less than 0.1 GMH. According to this aspect,the oligomer or polymer chain may be temperature sensitive and have atemperature-dependent affinity with the feed solvent.

According to at least one aspect of the present disclosure, the drawcompound may be a narrow distributed linear or branched random orsequential oligomer or polymer chain comprising ethylene oxide monomerand propylene oxide monomer. In such cases, the draw compound may have amolecular weight from about 1,200 to about 2,800 and an EO/PO ratio offrom 0.25 to 1.0, and a cloud point temperature from about 40° C. toabout 75° C. According to this aspect of the present disclosure, thedraw compound may further be characterized by a residual content lessthan 0.5% upon phase separation, a reverse diffusion through forwardosmosis (FO) membranes of less than 0.1 GMH. According to this aspect,the oligomer or polymer chain may be temperature sensitive and have atemperature-dependent affinity with the feed solvent.

According to at least one aspect of the present disclosure, the drawcompound may be a narrow distributed linear or branched random orsequential oligomer or polymer chain comprising ethylene oxide monomerand propylene oxide monomer. In such cases, the draw compound may have amolecular weight from about 800 to about 3,500 and an EO/PO ratio offrom 0.1 to 1.5, and a cloud point temperature from about 35° C. toabout 80° C. According to this aspect of the present disclosure, thedraw compound may further be characterized by a residual content lessthan 0.5% upon phase separation, a reverse diffusion through forwardosmosis (FO) membranes of less than 0.1 GMH. According to this aspect,the oligomer or polymer chain may be temperature sensitive and have atemperature-dependent affinity with the feed solvent.

According to at least one aspect of the present disclosure, the drawcompound may exhibit a reverse solute diffusion through forward osmosismembranes of from about 0.004 to about 0.01 GMH, or from about 0.01 toabout 0.02 GMH, or from about 0.02 to about 0.035 GMH, or from about0.004 GMH to about 0.035 GMH, or from about 0.004 GMH to about 0.1 GMH.

Within the constraints of osmotic pressure and cloud point temperature,the chemistry of the presently disclosed draw compounds may be selectedsuch to control the molecular weight and/or physical structure of thepolymer resulting in high rejection of the draw compound throughfiltration. In at least some instances, the draw compounds may beselected to cause the rejection of at least 90% of the draw compoundthrough filtration. In other cases, the draw compounds may be selectedto cause the rejection of at least 99% of the draw compound throughfiltration. In still other cases, the draw compounds may be selected tocause the rejection of at least 99.9% of the draw compound throughfiltration.

Further, the chemistry of the presently disclosed draw compounds may beselected to minimize back diffusion of the solute through a forwardosmosis membrane. In at least some instances, for salt waterdesalination, the osmotic pressure of a draw solution containing 50%draw compound in water is greater than 400 psi. In other instances, theosmotic pressure of the draw solution containing 50% draw compound inwater is greater than 550 psi. In still other instances, the osmoticpressure of the draw solution containing 50% draw compound in water isgreater than 700 psi.

In at least some instances, the molecular weight of the draw compound isgreater than 500. In other instances, the molecular weight of the drawcompound may begreater than 1000. In still other instances, themolecular weight of the draw compound may be greater than 2000.

The chain end of the presently disclosed oligomeric and polymeric drawcompound may undergo chemical alternation at operational and elevatedtemperatures with the reactive terminal group of hydroxyl, amine, andcarboxylic, and the like. End capping of the reactive terminal groupsenhances stability as well as modifies cloud point and osmotic pressureof the oligomeric and polymeric draw compounds. In at least someinstances, a C3 or propyl group is capped on one end of the linear EO-POcopolymer, and the cloud point is reduced by 17° C. In general, knownchemical reactions of hydroxyl, amine, and carboxylic groups can be usedin end capping, and the suitable capping groups include, but are notlimited to, allyl, phenyl, substituted or unsubstituted C1 to C14 alkylgroups, and substituted or unsubstituted aryl groups.

According to at least one aspect of the present disclosure, ananofilter, ultrafilter or reverse osmosis filter may be selected toobtain a molecular weight cutoff of less than 2000. In other cases, thefilter may be selected to obtain a molecular weight cutoff of less than1000. In still other cases, the filter may be selected to obtain amolecular weight cutoff of less than 500.

In at least some instances, the filter may be selected to obtain a NaClrejection of less than 50%. In other cases, the filter may be selectedto obtain a NaCl rejection of less than 25%. In still other cases, thefilter may be selected to obtain a NaCl rejection of less than 10%.

In at least some instances, the filter may be selected to obtain asolute rejection greater than 95%. In other instances, the filter may beselected to obtain a solute rejection of greater than 99%. In stillother instances, the filter may be selected to obtain a solute rejectionof greater than 99.9%. In other cases, the filter may be selected toobtain a solute rejection of greater than 99.99%.

Examples 1-8

Eight ethylene oxide-propylene oxide copolymers represented by Formula1-2 were synthesized in accordance to the synthesis procedure describedabove. The copolymers have a linear chain structure with random ethyleneoxide and propylene oxide distribution. The molecular weight of Examples1-8 are within the range of from 500 to 2,000, and the EO/PO ratio isfrom 0.25 to 1.0.

Examples 9-11

Five ethylene oxide-propylene oxide copolymers represented by Formula1-2 were synthesized in accordance to the synthesis procedure describedabove. The copolymers have a linear chain structure with random ethyleneoxide and propylene oxide distribution. The molecular weight of Examples9-11 are within the range of from 2,500 to 3,250, and the EO/PO ratio isfrom 0.53 to 1.0.

Examples 12-17

Six branched copolymers represented by Formulas 2-2, 2-3, and 2-4, weresynthesized in accordance to the synthesis procedure described above.The starting compounds used in the preparation of the branchedcopolymers were glycerol, trimetholpropane, pentaerythritol, andsorbitol. The copolymers have a linear chain structure with randomethylene-oxide and propylene oxide distribution. The molecular weight ofExamples 12-17 are within the range of from 1,200 to 2,500.

Evaluation of Osmotic Pressure

The draw solutions comprising the draw compounds of Examples 1-8 wereprepared to have various concentrations. The osmotic pressure of eachdraw solution was measured by using an osmotic pressure measurementinstrument (Vapro Vapor Pressure Osmometer, Model 5600, Wescor) inaccordance to the presently disclosed measurement method. Table 1 showsthe osmotic pressure measurements, as well as the molecular weight andEO/PO ratio for Examples 1-8. As shown in Table 1, the copolymers havinga high EO/PO ratio and a low molecular weight have a comparativelyhigher osmotic pressure.

TABLE 1 Draw Compound Molecular Weight (Daltons) EO/PO Ratio OsmoticPressure at 50% (psi) Example 1 TL-1180 500 1.0 1606 Example 2 TL-1180-11000 1.0 1052 Example 3 TL-1180-2 2000 1.0 817 Example 4 TL-1180-3 15001.0 978 Example 5 TL-1180-4 1500 0.25 443 Example 6 TL-1180-5 1500 0.35485 Example 7 TL-1180-6 1500 0.5 659 Example 8 TL-1180-7 1500 0.75 798

As shown in FIG. 3 , the osmotic pressure of all eight copolymersincreases sharply in concentrated state. Since a high osmotic pressureis the necessary condition to have a high solvent flux through asemipermeable membrane, one may be tempted to select the draw compoundwith the highest osmotic pressure. However, such a draw compound may notsatisfy the requirements of low reverse solute diffusion and low residuein solvent-rich phase after phase separation. Hence, a systematic viewis required in the selection of appropriate draw solutions.

The results of Table 1 and FIG. 2 confirm that a low molecular weightethylene oxide-propylene oxide draw compound with appropriate EO/POratio may generate an osmotic pressure as high as 1600 psi at aconcentration of 50% (Example 1). While other Example draw compoundshave their curves below that of Example 1, the workable osmotic pressurecan still be very high as long as a highly concentrated state can bereached upon draw solute regeneration. For example, Example 6 exhibitsan osmotic pressure of 1450 psi at 70% concentration, and estimated tobe above 2500 psi at 85% which can be achieved by a thermally inducedphase separation process using waste heat as energy source.

Determination of Cloud Point

The draw solutions comprising a copolymer of Examples 1-8 were preparedto have a 1.0 wt% aqueous concentration. The aqueous solutions wereheated at a heating rate of 0.5° C./min to at least 95° C. The onsettemperature at which each draw solution becomes cloudy visually orexhibits a sharp drop in transmittance light intensity was determined asthe cloud point. Table 2 shows the measurement results.

TABLE 2 Draw Compound Molecular Weight (Daltons) EO/PO Ratio Cloud Point(°C) Example 1 TL-1180 500 1.0 > 100° C. Example 2 TL-1180-1 10001.0 >100° C. Example 3 TL-1180-2 2000 1.0 80.5° C. Example 4 TL-1180-31500 1.0 93.5° C. Example 5 TL-1180-4 1500 0.25 52.0° C. Example 6TL-1180-5 1500 0.35 55.0° C. Example 7 TL-1180-6 1500 0.5 66.2° C.Example 8 TL-1180-7 1500 0.75 82.0° C.

As shown in Table 2, the draw compounds of Examples 1 to 8 have a cloudpoint from 52° C. to in excess of 100° C. Accordingly, these drawcompounds may phase separate in the temperature range of interest andcan be used in fluid purification and treatment systems. The copolymerswith a relatively low cloud point may be preferred for applications suchas portable drinking water production, sea water desalination, and wastewater treatment, while the copolymers with a relatively higher cloudpoint may be preferred for zero-liquid discharge fluid and high salinitywater treatment systems.

Determination of Residual Draw Compound

Residual draw compound in solvent-rich phase after thermal induced phaseseparation was determined by the following procedure. First, a 50 wt%temperature-sensitive draw compound solution was prepared. The solutionwas kept in room temperature for at least 2 hours to ensurehomogenization. Next, the homogeneous solution was placed in a heatedoven set at 85° C. to induce phase separation. For convenience, thesolution was heated in the oven overnight. Upon phase separation, asolvent-rich layer was present at the top and a distinct solute-richlayer was clearly visible at the bottom of a glass container. A samplevolume between 25- 30 mL was carefully taken out of the solvent-richlayer. In typical testing, the solvent may be water and the draw solutemay be an oligomer or polymer compound. The residual draw compound wasmeasured by total organic carbon (TOC) on a Shimadzu Total OrganicCarbon Analyzer (Model TOC-L). The results are compiled in Table 3.

TABLE 3 Draw Compound Molecular Weight (Daltons) Cloud Point (°C) TOC(ppm) Residue of draw solute Example 9 TL-1150 3250 48.0 495 0.099%Example 10 TL-1150-1 2800 69.8 4472 0.89% Example 11 TL-1150-2 2500 60.01500 0.30%

As shown in Table 3, it has been found that a slight increase inmolecular weight, combined with a reduced cloud point in the copolymers,unexpectedly produces a large impact in the residual draw compound levelafter thermally induced phase separation, as evidenced by the drop ofresidual concentration from 0.89% for Example 10 to 0.099% for theExample 9 draw compound.

Evaluation of Membrane Performance

Membrane flux and reverse solute diffusion evaluation in forward osmosismode is conducted with respect to the draw solutions includingcopolymers of Examples 10-15, respectively, in accordance with thefollowing testing procedure. The membrane flux was determined with aMembrane Testing Fixture (Model II) designed and manufactured by TreviSystems, and a Toyobo cellulose triacetate (CTA) hollow fiber FO modulewas utilized as a semi-permeable membrane. De-ionized water was fed as afeed solution and a 50 wt% draw compound solution wass used as the drawsolution. The volumetric flow rates of feed and draw solutions wereselected to be close to the flow rates in commercial 5″ and 10″ hollowfiber membrane elements. The feed solution was faced toward the activelayer of the hollow fibers. Both feed and draw solutions were circulatedin close loops for at least 4 hours. The water flux and reverse solutediffusion were determined at the run time of 4 hours. The reverse solutediffusion from draw to feed solution through the membrane was measuredby total organic carbon (TOC). The results are summarized in Table 4.

TABLE 4 Polymer Molecular Weight (Daltons) Structure Flux in FO Mode(LMH) Reverse Solute Diffusion (GMH) Example 10 TL-1150-1 2800 Linear0.68 0.0326 Example 11 TL-1150-2 2500 Linear 0.65 0.0298 Example 12TL-1371 2500 3-arm 0.68 0.0154 Example 13 TL-1374 2500 3-arm 0.70 0.0092Example 14 TL-1373 2500 4-arm 0.71 0.0149 Example 15 TL-1379 2500 6-arm0.72 0.0048

Comparative measurements on membrane performance in FO and PRO (pressureretarded osmosis) modes were performed on Example 10 and Example 11 drawcompounds. The tests differed in that the feed solution was faced towardthe active layer of the semi-permeable membrane in FO mode while thedraw solution was in contact with the active layer of the semi-permeablemembrane in PRO mode. The results are shown in Table 5.

TABLE 5 Polymer Molecular Weight (Daltons) Flux in FO Mode (LMH) ReverseSolute Diffusion in FO Mode (GMH) Flux in PRO Mode (LMH) Reverse SoluteDiffusion in PRO Mode (GMH) Example 10 TL-1150-1 2800 0.68 0.0326 1.40.0186 Example 11 TL-1150-2 2500 0.65 0.0298 1.5 0.0137

It is apparent that superior membrane performance is realized in PROmode in comparison to the FO mode. The flux is more than doubled and thereverse solute diffusion is cut to half in PRO mode comparatively. Whileit may be advantageous to perform the forward osmotic fluid treatmentprocess in PRO mode in certain applications, such a mode may not bepractical due to the tendency of membrane fouling which is the result ofdirect contact of feed fluid to the support layer of the semipermeablemembranes.

It should be noted that the flux in Table 5 is the result of themembrane testing procedure used herein, and may not be representative ofresults achieved in a practical forward osmosis process. As shown inFIG. 3 , the phase diagram of Example 11 indicates that the drawcompound can be regenerated by up to 85% at a temperature of 85° C.Although a direct measurement is not available, the osmotic pressure ofExample 11 is estimated to be above 2,500 psi at 85% concentrationcompared to approximately 620 psi at 50%. Thus, the flux through asemipermeable membrane is expected to be much higher when a concentratedsolution higher than 50% is utilized as the draw solution.

Flux Evaluation of Low Molecular Weight Branched Draw Compounds

Low molecular weight branched draw compounds were synthesized whereinExample 18 and Example 19 were 3-arm and a 4-arm random ethyleneoxide-propylene oxide copolymers, respectively. Molecular weight anddistribution were analyzed by a Shimadzu LC-20AD LiquidChromatograph/Gel Permeation Chromatograph (GPC) equipped with SIL-20Aauto sampler, DGU-20A degassing unit, DID-10A refractive index detector,CTO-20AC column oven, CBM-20A communication bus module, and LCsolutionsoftware. The column bank includes three Phenomenex Phenogel 5 µ GPCcolumns with a pore size of 50 Å, 500 Å, and 10⁴ Å. The number-averagemolecular weight (M_(n)) and weight average molecular weight (M_(w)) ofthe copolymer were calculated based on polyethylene glycol standardscalibration. The molecular characteristics are summarized in Table 6.

TABLE 6 Draw Compound Mn M_(W) M_(w) / M_(n) Example 18 TL-1435 14791568 1.06 Example 19 DLW-1600 1177 1250 1.07

The flux through the semi-permeable membrane was determined inaccordance to the testing procedure described previously with respect toExamples 18 and 19 above. Again, a 50 wt% draw compound solution wasused as the draw solution while de-ionized water was used as the feedsolution. As shown in Table 7, the flux at run time of 4 hours is 0.92LMH, which was 42% higher as compared to the linear polymer of Example11.

TABLE 7 Polymer Flux in FO Mode (LMH) Reverse Solute Diffusion in FOMode (GMH) Flux in PRO Mode (LMH) Reverse Solute Diffusion in PRO Mode(GMH) Example 18 TL-1435 1.3 0.0065 Example 19 0.92 0.128 1.5 0.044DLW-1600

Evaluation of End-Capped Draw Compounds

Exemplary one end-capped C1 (methyl) and C3 (propyl) random ethyleneoxide-propylene oxide copolymers were evaluated in accordance to thestandard testing procedure. The results are compiled in Table 8 andcompared to a reference draw compound of linear EO-PO copolymer with thesame molecular weight and terminal hydroxyl groups at both chain ends.

TABLE 8 Draw Compound End Capping Osmotic Pressure at 50% (psi) OsmoticPressure at 70% (psi) Cloud Point (°C) Example 20 TL-1300 C1, one end567 1156 56 Example 21 TL-1301 C3, one end 476 952 45 Reference(TL-1150-2) None 586 1277 62

According to at least one aspect of the present disclosure, a method forpurifying or treating a feed solution using the presently disclosed drawcompounds and solutions is provided. FIG. 5 is a flow chart describing amethod 500 of using the presently disclosed draw compound to purify ortreat a feed solution, according to a forward osmosis process. Referringto FIG. 5 , a flow chart is presented in accordance with an exampleembodiment. The example method shown in FIG. 5 is provided by way of anexample, as there are a variety of ways to carry out the method. Theillustrated order of blocks is illustrative only and the order of theblocks can change according to the present disclosure. Additional blockscan be added or fewer blocks can be utilized, without departing fromthis disclosure.

The method 500 can begin at block 505. At block 505, a semipermeablemembrane having a feed side and a draw side is provided. At block 510, afeed solution comprising a solvent and having a first osmotic pressureis provided. A draw solution comprising a draw compound and having asecond osmotic pressure is provided at block 515. At block 520, at leasta portion of the solvent of the feed solution is caused to betransported from the feed side through the semipermeable membrane toproduce a dilute draw solution on the draw side of the semipermeablemembrane. The diluted draw solution is heated at block 525 so as toinitiate phase separation and produce a two phase effluent streamcomprising a liquid phase of draw compound and a liquid phase ofsolvent. At block 530, the draw compound is caused to agglomerate in thediluted draw solution to produce an agglomerated two-phase effluentstream comprising a liquid phase of agglomerated draw compound and aliquid phase of solvent. The agglomerated draw compound is separatedfrom the diluted draw solution at block 535 to produce a solvent richstream, comprising residual draw compound and solvent, and a solute richstream, comprising agglomerated draw compound and solvent. At block 540,the solvent rich stream is cooled to produce a cooled single phasesolvent rich stream comprising the residual draw compound. At block 545,the residual draw compound is separated from the cooled single phasesolvent rich stream to produce a residual draw compound stream and apurified solvent product stream. In at least some instances, the solventmay be water. For instance, the method 500 may be used to treat orpurify sea water, brackish water, industrial and municipal waste water,contaminated water, and the like.

Example embodiments have been described hereinabove regarding improvedsystems and processes for forward osmosis water purification ordesalination. The embodiments shown and described above are onlyexamples. Therefore, many such details are neither shown nor described.Even though numerous characteristics and advantages of the presenttechnology have been set forth in the foregoing description, togetherwith details of the structure and function of the present disclosure,the disclosure is illustrative only, and changes may be made in thedetail, especially in matters of shape, size and arrangement of theparts within the principles of the present disclosure to the full extentindicated by the broad general meaning of the terms used in the attachedclaims. Various modification to and departure from the disclosed exampleembodiments will occur to those having ordinary skill in the art. Itwill therefore be appreciated that the embodiments described above maybe modified within the scope of the appended claims.

Statements of the Disclosure Include

Statement 1: A draw compound for osmotic fluid purification, the drawcompound comprising: a linear random, sequential, or block molecularchain including at least one oxides monomer or diol monomer, wherein themolecular chain including the at least one epoxide monomer or diolmonomer, is temperature-sensitive and has a temperature-dependentaffinity with a feed solvent, and wherein the draw compound furthercomprises a first terminal group and a second terminal group, at leastone of the first terminal group and the second terminal group selectedfrom the group consisting of a hydroxyl group, an amine group, acarboxylic group, an allyl group, and a C1 to C14 substituted andunsubstituted alky group.

Statement 2: A draw compound according to Statement 1, wherein the atleast one oxide monomer is selected from the group consisting ofethylene oxide, propylene oxide, 1,2-epoxy-butane, 2,3-epoxy-butane,styrene oxide, epifluohydrin, epichlorohydrin, tetrahydrofuran, oxetane,dioxilane, trioxane, butyl glycidyl ether, phenyl glycidyl ether, andallyl glycidyl ether.

Statement 3: A draw compound according to Statement 1 or Statement 2,wherein the at least one diol monomer is selected from the groupconsisting of 1,2-ethanediol, 1,2-propanediol, 1,3-propanediol,1,4-butanediol, 1,5-pentanediol, 2-methyl-2-propyl-1,3-propanediol,neopentyl glycol, resorcinol, and 4,4′-(propane-2,2-diyl)diphenol.

Statement 4: A draw compound according to any one of the precedingStatements 1-3, wherein the draw compound is a linear random oligomer orcopolymer of ethylene oxide, propylene oxide, and butylene oxide.

Statement 5: A draw compound according to any one of the precedingStatements 1-4, wherein the draw compound is a linear random oligomer orcopolymer of ethylene oxide and propylene oxide.

Statement 6: A draw compound according to any one of the precedingStatements 1-5, wherein the draw compound has a molecular weight of from100 to 25,000.

Statement 7: A draw compound according to any one of the precedingStatements 1-5, wherein the draw compound has a molecular weight of from200 to 5,000.

Statement 8: A draw compound according to any one of the precedingStatements 1-5, wherein the draw compound has a molecular weight of from500 to 3,500.

Statement 9: A draw compound according to any one of the precedingStatements 1-5, wherein the draw compound has a molecular weight of from800 to 2,800.

Statement 10: A draw compound according to any one of the precedingStatements 1-9, wherein the draw compound has an EO/PO ratio from 0.01to 10.0.

Statement 11: A draw compound according to any one of the precedingStatements 1-9, wherein the draw compound has an EO/PO ratio from 0.05to 5.0.

Statement 12: A draw compound according to any one of the precedingStatements 1-9, wherein the draw compound has an EO/PO ratio from 0.1 to1.0.

Statement 13: A draw compound according to any one of the precedingStatements 1-12, wherein the draw compound has a cloud point temperaturefrom 20° C. to 175° C.

Statement 14: A draw compound according to any one of the precedingStatements 1-12, wherein the draw compound has a cloud point temperaturefrom 35° C. to 125° C.

Statement 15: A draw compound according to any one of the precedingStatements 1-12, wherein the draw compound has a cloud point temperaturefrom 40° C. to 80° C.

Statement 16: A draw compound for osmotic fluid purification, the drawcompound comprising: a branched random, sequential, or block molecularchain including at least one oxide monomer or diol monomer, wherein themolecular chain including at least one oxide monomer or diol monomer istemperature-sensitive and has a temperature-dependent affinity with afeed solvent, and wherein the draw compound further comprises a firstterminal group and a second terminal group, at least one of the firstterminal group and the second terminal group selected from the groupconsisting of a hydroxyl group, an amine group, a carboxylic group, anallyl group, and a C1 to C14 substituted and unsubstituted alky group.

Statement 17: A draw compound according to Statement 16, wherein thedraw compound has three or more branches, each branch comprising one ormore epoxide monomers selected from of the group consisting of ethyleneoxide, propylene oxide, 1,2-epoxy-butane, 2,3-epoxy-butane, styreneoxide, epifluohydrin, epichlorohydrin, tetrahydrofuran, oxetane,dioxilane, trioxane, butyl glycidyl ether, phenyl glycidyl ether, andallyl glycidyl ether.

Statement 18: A draw compound according to Statement 16, wherein thedraw compound has three or more branches, each branch comprising one ormore diol monomers selected from the group consisting of 1,2-ethanediol,1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol,2-methyl-2-propyl-1,3-propanediol, neopentyl glycol, resorcinol, and4,4′-(propane-2,2-diyl)diphenol.

Statement 19: A draw compound according to any one of the precedingStatements 16-18, wherein the starting compound for the preparation ofthe draw compound is selected from the group consisting of vitamins andsugar alcohols.

Statement 20: A draw compound according to any one of the precedingStatements 16-18, wherein the starting compound for the preparation ofthe draw compound is selected from the group consisting of polyols,glycerol, trimethylolpropane, pentaerythritol, diglycerol,ditrimethylolpropane, phloroglucinol, sorbitol, sorbitan, glucose,fructose, and methyl glucoside.

Statement 21: A draw compound according to any one of the precedingStatements 16-18, wherein the starting compound for the preparation ofthe draw compound is selected from the group consisting of ascorbicacid, glycerol, erythritol, threitol arabitol, ribitol, xylitol,fructitol, galacititol, iditol, inositol, mannitol, sorbitol, volemitol,isomalt, maltitol, and lactitol.

Statement 22: A draw compound according to any one of the precedingStatements 16-21, wherein the draw compound is a branched randomoligomer or copolymer of ethylene oxide, propylene oxide, and butyleneoxide.

Statement 23: A draw compound according to any one of the precedingStatements 16-21, wherein the draw compound is a branched randomoligomer or copolymer of ethylene oxide and propylene oxide.

Statement 24: A draw compound according to any one of the precedingStatements 16-23, wherein the draw compound has a molecular weight from100 to 25,000.

Statement 25: A draw compound according to any one of the precedingStatements 16-23, wherein the draw compound has a molecular weight from200 to 5,000.

Statement 26: A draw compound according to any one of the precedingStatements 16-23, wherein the draw compound has a molecular weight from500 to 3,500.

Statement 27: A draw compound according to any one of the precedingStatements 16-23, wherein the draw compound has a molecular weight offrom 800 to 2,800.

Statement 28: A draw compound according to any one of the precedingStatements 16-27, wherein the draw compound has an EO/PO ratio from 0.01to 10.0.

Statement 29: A draw compound according to any one of the precedingStatements 16-27, wherein the draw compound has an EO/PO ratio from0.05-5.0.

Statement 30: A draw compound according to any one of the precedingStatements 16-27, wherein the draw compound has an EO/PO ratio from0.1-1.0.

Statement 31: A draw compound according to any one of the precedingStatements 16-30, wherein the draw compound has a cloud pointtemperature from 20° C. to 100° C.

Statement 32: A draw compound according to any one of the precedingStatements 16-30, wherein the draw compound has a cloud pointtemperature from 35° C. to 125° C.

Statement 33: A draw compound according to any one of the precedingStatements 16-30, wherein the draw compound has a cloud pointtemperature from 40° C. to 80° C.

Statement 34: A draw compound according to Statement 23, wherein thedraw compound is a 3-arm branched random oligomer or copolymer and thestarting compound is glycerol.

Statement 35: A draw compound according to Statement 23, wherein thedraw compound is a 3-arm branched random oligomer or copolymer and thestarting compound is trimethylolpropane.

Statement 36: A draw compound according to Statement 23, wherein thedraw compound is a 4-arm branched random oligomer or copolymer and thestarting compound is pentaerythritol.

Statement 37: A draw compound according to Statement 23, wherein thedraw compound is a 6-arm branched random oligomer or copolymer and thestarting compound is sorbitol.

Statement 38: A draw solution for osmotic fluid purification, the drawsolution comprising the draw compound according to of any of thepreceding Statements 1-37.

Statement 39: A system for purifying water, the system comprising: afeed solvent source; a draw solution comprising a draw compound; asemipermeable membrane comprising a feed side for receiving, from thefeed solvent source, a feed solvent stream having a first osmoticpressure and a draw side for receiving the draw solution having a secondosmotic pressure, wherein a diluted draw solution stream is producedwhen solvent passes from the feed solvent stream to the draw side viathe semipermeable membrane; wherein the draw compound comprises a linearrandom, sequential, or block molecular chain consisting of at least oneepoxide monomer or diol monomer, wherein the molecular chain includingat least one epoxide monomer or diol monomer, is temperature-sensitiveand has a temperature-dependent affinity with a feed solvent, andwherein the draw compound further comprises a first terminal group and asecond terminal group, at least one of the first terminal group and thesecond terminal group selected from the group consisting of a hydroxylgroup, an amine group, a carboxylic group, an allyl group, and a C1 toC14 substituted and unsubstituted alky group.

Statement 40: A system according to Statement 39, further comprising: afirst heat exchanger to heat the diluted draw solution stream; acoalescer configured to agglomerate the draw compound in the diluteddraw solution stream to produce an agglomerated two phase effluentstream comprising a liquid phase of agglomerated draw compound and aliquid phase of solvent; a liquid phase separator capable of separatingtwo or more immiscible liquids or solutions, the liquid phase separatorconfigured to separate agglomerated draw compound from the agglomeratedtwo phase effluent stream to produce a solvent rich stream comprisingsolvent and residual draw compound, and a draw compound rich streamcomprising the agglomerated draw compound and solvent; a second heatexchanger for cooling the solvent rich stream to produce a cooled singlephase solvent rich stream; and a filtration module for separating theresidual draw compound from the cooled single phase solvent rich streamto produce a residual draw compound stream and a purified solventproduct stream.

Statement 41: A system according to Statement 40, wherein the filtrationmodule is selected from the group consisting of a nanofilter, anultrafilter, and a reverse osmosis module.

Statement 42: A system according to any one of the preceding Statements39-41, wherein the at least one oxide monomer is selected from the groupconsisting of ethylene oxide, propylene oxide, 1,2-epoxy-butane,2,3-epoxy-butane, styrene oxide, epifluohydrin, epichlorohydrin,tetrahydrofuran, oxetane, dioxilane, trioxane, butyl glycidyl ether,phenyl glycidyl ether, and allyl glycidyl ether.

Statement 43: A system according to any one of the preceding Statements39-42, wherein the at least one diol monomer is selected from the groupconsisting of 1,2-ethanediol, 1,2-propanediol, 1,3-propanediol,1,4-butanediol, 1,5-pentanediol, 2-methyl-2-propyl-1,3-propanediol,neopentyl glycol, resorcinol, and 4,4′-(propane-2,2-diyl)diphenol.

Statement 44: A system according to any one of the preceding Statements39-43, wherein the draw compound is a linear random oligomer orcopolymer of ethylene oxide, propylene oxide, and butylene oxide.

Statement 45: A system according to any one of the preceding Statements39-43, wherein the draw compound is a linear random oligomer orcopolymer of ethylene oxide and propylene oxide.

Statement 46: A system according to any one of the preceding Statements39-45, wherein the draw compound has a molecular weight of from 100 to25,000.

Statement 47: A system according to any one of the preceding Statements39-46, wherein the draw compound has an EO/PO ratio from 0.01 to 10.0.

Statement 48: A system according to any one of the preceding Statements39-47, wherein the draw compound has a cloud point temperature from 20°C. to 175° C.

Statement 49: A system for purifying a solution, the system comprising:a feed solvent source; a draw solution comprising a draw compound; asemipermeable membrane comprising a feed side for receiving, from thefeed solvent source, a feed solvent stream having a first osmoticpressure and a draw side for receiving the draw solution having a secondosmotic pressure, wherein a diluted draw solution stream is producedwhen solvent passes from the feed solvent stream to the draw side viathe semipermeable membrane; wherein the draw compound comprises abranched random, sequential, or block molecular chain consisting of atleast one oxide monomer or diol monomer, wherein the molecular chainincluding at least one oxide monomer or diol monomer istemperature-sensitive and has a temperature-dependent affinity with afeed solvent, and wherein the draw compound further comprises a firstterminal group and a second terminal group, at least one of the firstterminal group and the second terminal group selected from the groupconsisting of a hydroxyl group, an amine group, a carboxylic group, anallyl group, and a C1 to C14 substituted and unsubstituted alky group.

Statement 50: A system according to Statement 49, further comprising: afirst heat exchanger to heat the diluted draw solution stream; acoalescer configured to agglomerate the draw compound in the diluteddraw solution stream to produce an agglomerated two phase effluentstream comprising a liquid phase of agglomerated draw compound and aliquid phase of solvent; a liquid phase separator capable of separatingtwo or more immiscible liquids or solutions, the liquid phase separatorconfigured to separate agglomerated draw compound from the agglomeratedtwo phase effluent stream to produce a solvent rich stream comprisingsolvent and residual draw compound, and a draw compound rich streamcomprising the agglomerated draw compound and solvent; a second heatexchanger for cooling the solvent rich stream to produce a cooled singlephase solvent rich stream; and a filtration module for separating theresidual draw compound from the cooled single phase solvent rich streamto produce a residual draw compound stream and a purified solventproduct stream.

Statement 51: A system according to Statement 50, wherein the filtrationmodule is selected from the group consisting of a nanofilter, anultrafilter, and a reverse osmosis module.

Statement 52: A system according to any one of the preceding Statements49-51, wherein the draw compound has three or more branches, each branchcomprising one or more epoxide monomers selected from of the groupconsisting of ethylene oxide, propylene oxide, 1,2-epoxy-butane,2,3-epoxy-butane, styrene oxide, epifluohydrin, epichlorohydrin,tetrahydrofuran, oxetane, dioxilane, trioxane, butyl glycidyl ether,phenyl glycidyl ether, and allyl glycidyl ether.

Statement 53: A system according to any one of the preceding Statements49-51, wherein the draw compound has three or more branches, each branchcomprising one or more diol monomers selected from the group consistingof 1,2-ethanediol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol,1,5-pentanediol, 2-methyl-2-propyl-1,3-propanediol, neopentyl glycol,resorcinol, and 4,4′-(propane-2,2-diyl)diphenol.

Statement 54: A system according to any one of the preceding Statements49-53, wherein the draw compound is a branched random oligomer orcopolymer of ethylene oxide, propylene oxide, and butylene oxide.

Statement 55: A system according to any one of the preceding Statements49-53, wherein the draw compound is a branched random oligomer orcopolymer of ethylene oxide and propylene oxide.

Statement 56: A system according to any one of the preceding Statements49-55, wherein the draw compound has a molecular weight from 100 to25,000.

Statement 57: A system according to any one of the preceding Statements49-56, wherein the draw compound has an EO/PO ratio from 0.01 to 10.0.

Statement 58: A system according to any one of the preceding Statements49-57, wherein the draw compound has a cloud point temperature from 20°C. to 175° C.

Statement 59: A method for purifying or treating a feed solution, themethod comprising: providing a semipermeable membrane having a feed sideand a draw side; providing a feed solution comprising a solvent andhaving a first osmotic pressure; providing a draw solution comprising adraw compound and having a second osmotic pressure, wherein the drawcompound comprises a branched random, sequential, or block molecularchain consisting of at least one oxide monomer or diol monomer, whereinthe molecular chain including at least one oxide monomer or diol monomeris temperature-sensitive and has a temperature-dependent affinity with afeed solvent, and wherein the draw compound further comprises a firstterminal group and a second terminal group, at least one of the firstterminal group and the second terminal group selected from the groupconsisting of a hydroxyl group, an amine group, a carboxylic group, anallyl group, and a C1 to C14 substituted and unsubstituted alky group;causing the solvent to be transported from the feed side through thesemipermeable membrane to produce a dilute draw solution on the drawside of the semipermeable membrane; heating the diluted draw solution toinitiate phase separation and produce a two phase effluent streamcomprising a liquid phase of draw compound and a liquid phase ofsolvent; causing the draw compound to agglomerate in the diluted drawsolution to produce an agglomerated two-phase effluent stream comprisinga liquid phase of agglomerated draw compound and a liquid phase ofsolvent; separating the agglomerated draw compound from the diluted drawsolution to produce a solvent rich stream, comprising residual drawcompound and solvent, and a solute rich stream, comprising agglomerateddraw compound and solvent; cooling the solvent rich stream to produce acooled single phase solvent rich stream comprising the residual drawcompound; and separating the residual draw compound from the cooledsingle phase solvent rich stream to produce a residual draw compoundstream and a purified solvent product stream.

Statement 60: A method according to Statement 59, wherein the drawcompound has three or more branches, each branch comprising one or moreepoxide monomers selected from of the group consisting of ethyleneoxide, propylene oxide, 1,2-epoxy-butane, 2,3-epoxy-butane, styreneoxide, epifluohydrin, epichlorohydrin, tetrahydrofuran, oxetane,dioxilane, trioxane, butyl glycidyl ether, phenyl glycidyl ether, andallyl glycidyl ether.

Statement 61: A method according to Statement 59, wherein the drawcompound has three or more branches, each branch comprising one or morediol monomers selected from the group consisting of 1,2-ethanediol,1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol,2-methyl-2-propyl-1,3-propanediol, neopentyl glycol, resorcinol, and4,4′-(propane-2,2-diyl)diphenol.

Statement 62: A method according to Statement 59, wherein the drawcompound is a branched random oligomer or copolymer of ethylene oxide,propylene oxide, and butylene oxide.

Statement 63: A method according to Statement 59, wherein the drawcompound is a branched random oligomer or copolymer of ethylene oxideand propylene oxide.

Statement 64: A method according to any one of the preceding Statements59-63, wherein the draw compound has a molecular weight from 100 to25,000.

Statement 65: A method according to any one of the preceding Statements59-64, wherein the draw compound has an EO/PO ratio from 0.01 to 10.0.

Statement 66: A method according to any one of the preceding Statements59-63, wherein the draw compound has a cloud point temperature from 20°C. to 175° C.

Statement 67: A draw compound for osmotic fluid purification, the drawcompound comprising: a narrow distributed linear or branched random orsequential oligomer or polymer chain comprising ethylene oxide monomerand propylene oxide monomer.

Statement 68: A draw compound according to Statement 67, wherein thedraw compound has a molecular weight of from 500 to 3,500.

Statement 69: A draw compound according to Statement 67, wherein thedraw compound has a molecular weight of from 800 to 3,000.

Statement 70: A draw compound according to Statement 67, wherein thedraw compound has a molecular weight of from 1,200 to 2,800.

Statement 71: A draw compound according to Statement 67, wherein thedraw compound has a molecular weight of from 800 to 2,800.

Statement 72: A draw compound according to any one of the precedingStatements 67-71, wherein the draw compound has an EO/PO ratio from 0.01to 10.0.

Statement 73: A draw compound according to any one of the precedingStatements 67-71, wherein the draw compound has an EO/PO ratio from 0.1to 1.5.

Statement 74: A draw compound according to any one of the precedingStatements 67-71, wherein the draw compound has an EO/PO ratio from 0.25to 1.0.

Statement 75: A draw compound according to any one of the precedingStatements 67-74, wherein the draw compound has a cloud pointtemperature from 20° C. to 100° C.

Statement 76: A draw compound according to any one of the precedingStatements 67-74, wherein the draw compound has a cloud pointtemperature from 35° C. to 80° C.

Statement 77: A draw compound according to any one of the precedingStatements 67-74, wherein the draw compound has a cloud pointtemperature from 40° C. to 75° C.

Statement 78: A draw compound according to any one of the precedingStatements 67-77, wherein the draw compound exhibits a residual contentless than 0.5% upon phase separation.

Statement 79: A draw compound according to any one of the precedingStatements 67-78, wherein the draw compound exhibits a reverse solutediffusion through forward osmosis membranes of from about 0.004 to about0.01 GMH.

Statement 80: A draw compound according to any one of the precedingStatements 67-78, wherein the draw compound exhibits a reverse solutediffusion through forward osmosis membranes of from about 0.01 to about0.02 GMH.

Statement 81: A draw compound according to any one of the precedingStatements 67-78, wherein the draw compound exhibits a reverse solutediffusion through forward osmosis membranes of from about 0.02 to about0.035 GMH.

Statement 82: A draw compound according to any one of the precedingStatements 67-78, wherein the draw compound exhibits a reverse solutediffusion through forward osmosis membranes of from about 0.004 GMH toabout 0.035 GMH.

Statement 83: A draw compound according to any one of the precedingStatements 67-78, wherein the draw compound exhibits a reverse solutediffusion through forward osmosis membranes of from about 0.004 GMH toabout 0.1 GMH.

Statement 84: A draw compound according to any one of the precedingStatements 67-78, wherein the draw compound exhibits a reverse solutediffusion through forward osmosis membranes of less than 0.1 GMH.

Statement 85: A draw compound according to any one of the precedingStatements 67-84, wherein the oligomer or polymer chain of the drawcompound is temperature sensitive and has a temperature-dependentaffinity with the feed solvent.

Statement 86: A system for purifying water, the system comprising: afeed solvent source; a draw solution comprising a draw compoundaccording to any one of Statements 1-37 or Statements 67-85; asemipermeable membrane comprising a feed side for receiving, from thefeed solvent source, a feed solvent stream having a first osmoticpressure and a draw side for receiving the draw solution having a secondosmotic pressure, wherein a diluted draw solution stream is producedwhen solvent passes from the feed solvent stream to the draw side viathe semipermeable membrane.

Statement 87: A system according to Statement 86, further comprising: afirst heat exchanger to heat the diluted draw solution stream; acoalescer configured to agglomerate the draw compound in the diluteddraw solution stream to produce an agglomerated two phase effluentstream comprising a liquid phase of agglomerated draw compound and aliquid phase of solvent; a liquid phase separator capable of separatingtwo or more immiscible liquids or solutions, the liquid phase separatorconfigured to separate agglomerated draw compound from the agglomeratedtwo phase effluent stream to produce a solvent rich stream comprisingsolvent and residual draw compound, and a draw compound rich streamcomprising the agglomerated draw compound and solvent; a second heatexchanger for cooling the solvent rich stream to produce a cooled singlephase solvent rich stream; and a filtration module for separating theresidual draw compound from the cooled single phase solvent rich streamto produce a residual draw compound stream and a purified solventproduct stream.

Statement 88: A method for purifying or treating a feed solution, themethod comprising: providing a semipermeable membrane having a feed sideand a draw side; providing a feed solution comprising a solvent andhaving a first osmotic pressure; providing a draw solution comprising adraw compound according to any one of the Statements 1-37 or 67-85 andhaving a second osmotic pressure; causing the solvent to be transportedfrom the feed side through the semipermeable membrane to produce adilute draw solution on the draw side of the semipermeable membrane;heating the diluted draw solution to initiate phase separation andproduce a two phase effluent stream comprising a liquid phase of drawcompound and a liquid phase of solvent; causing the draw compound toagglomerate in the diluted draw solution to produce an agglomeratedtwo-phase effluent stream comprising a liquid phase of agglomerated drawcompound and a liquid phase of solvent; separating the agglomerated drawcompound from the diluted draw solution to produce a solvent richstream, comprising residual draw compound and solvent, and a solute richstream, comprising agglomerated draw compound and solvent; cooling thesolvent rich stream to produce a cooled single phase solvent rich streamcomprising the residual draw compound; and separating the residual drawcompound from the cooled single phase solvent rich stream to produce aresidual draw compound stream and a purified solvent product stream.

What is claimed is:
 1. A draw compound for osmotic fluid purification,the draw compound comprising: a linear random, sequential, or blockmolecular chain including at least one oxide monomer selected from thegroup consisting of styrene oxide, epifluorohydrin, epichlorohydrin,oxetane, dioxilane, trioxane, butyl glycidyl ether, phenyl glycidylether, and allyl glycidyl ether, wherein the at least one oxide monomeris temperature-sensitive and has a temperature-dependent affinity with afeed solvent, and wherein the draw compound further comprises a firstterminal group and a second terminal group, at least one of the firstterminal group and the second terminal group selected from the groupconsisting of a hydroxyl group, an amine group, a carboxylic group, anallyl group, and a C1 to C14 substituted and unsubstituted alkyl group.2. The draw compound according to claim 1, wherein the draw compound isa linear random oligomer or copolymer of ethylene oxide, propyleneoxide, and butylene oxide.
 3. The draw compound according to claim 1,wherein the draw compound is a linear random oligomer or copolymer ofethylene oxide and propylene oxide.
 4. The draw compound according toclaim 3, wherein the draw compound has a molecular weight of from 100 to25,000.
 5. The draw compound according to claim 3, wherein the drawcompound has an EO/PO ratio from 0.01 to 10.0.
 6. The draw compoundaccording to claim 3, wherein the draw compound has a molecular weightof from 200 to 5,000.
 7. The draw compound according to claim 3, whereinthe draw compound has a molecular weight of from 500 to 3,500.
 8. Thedraw compounds according to claim 3, wherein the draw compound has amolecular weight of from 800 to 2,800.
 9. The draw compound according toclaim 3, wherein the draw compound has an EO/PO ratio from 0.01 to 10.0.10. The draw compound according to claim 3, wherein the draw compoundhas an EO/PO ratio from 0.05 to 5.0.
 11. The draw compound according toclaim 3, wherein the draw compound has an EO/PO ratio from 0.1 to 1.0.12. The draw compound according to claim 3, wherein the draw compoundhas a cloud point temperature from 20° C. to 175° C.
 13. The drawcompound according to claim 3, wherein the draw compound has a cloudpoint temperature from 35° C. to 125° C.
 14. The draw compound accordingto claim 3, wherein the draw compound has a cloud point temperature from40° C. to 80° C.
 15. A draw compound for osmotic fluid purification, thedraw compound comprising: a branched random, sequential, or blockmolecular chain including at least one oxide monomer or diol monomer,wherein the molecular chain including at least one oxide monomer or diolmonomer is temperature-sensitive and has a temperature-dependentaffinity with a feed solvent, and wherein the draw compound furthercomprises a first terminal group and a second terminal group, at leastone of the first terminal group and the second terminal group selectedfrom the group consisting of a hydroxyl group, an amine group, acarboxylic group, an allyl group, and a C1 to C14 substituted andunsubstituted alkyl group.
 16. The draw compound according to claim 15,wherein the draw compound has three or more branches, each branchcomprising one or more epoxide monomers selected from of the groupconsisting of ethylene oxide, propylene oxide, 1,2-epoxy-butane,2,3-epoxy-butane, styrene oxide, epifluohydrin, epichlorohydrin,tetrahydrofuran, oxetane, dioxilane, trioxane, butyl glycidyl ether,phenyl glycidyl ether, and allyl glycidyl ether or each branchcomprising one or more diol monomers selected from the group consistingof 1,2-ethanediol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol,1,5-pentanediol, 2-methyl-2-propyl-1,3-propanediol, neopentyl glycol,resorcinol, and 4,4′-(propane-2,2-diyl)diphenol.
 17. The draw compoundaccording to claim 15, wherein the starting compound for the preparationof the draw compound is selected from the group consisting of vitaminsand sugar alcohols.
 18. The draw compound according to claim 15, whereinthe starting compound for the preparation of the draw compound isselected from the group consisting of polyols, glycerol,trimethylolpropane, pentaerythritol, diglycerol, ditrimethylolpropane,phloroglucinol, sorbitol, sorbitan, glucose, fructose, and methylglucoside, or selected from the group consisting of ascorbic acid,glycerol, erythritol, threitol arabitol, ribitol, xylitol, fructitol,galacititol, iditol, inositol, mannitol, sorbitol, volemitol, isomalt,maltitol, and lactitol.
 19. The draw compound according to claim 15,wherein the draw compound is a branched random oligomer or copolymer ofethylene oxide, propylene oxide, and butylene oxide or copolymer ofethylene oxide and propylene oxide.
 20. The draw compound according toclaim 15, wherein the draw compound has an EO/PO ratio from 0.01 to10.0.